Wideband beamformer system

ABSTRACT

An adaptive phased-array processing solution, referred to as the Wideband Beamformer System (WBS), demonstrates an improvement in the range and quality of air link surveillance downlink wireless cell radio signals. The WBS applies wideband frequency-domain adaptive beamforming to preprocess the dense RF signal environment, minimizing co-channel interference (CCI) from each signal, and then reconstructing a “clean” version of the signal for input to the existing surveillance receiver(s).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority to similarlytitled U.S. Provisional Patent Application No. 61/893,701 filed Oct. 21,2013, the contents of which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE EMBODIMENTS

1. Field of the Embodiments

The embodiments described and illustrated herein are directed to a toolfor improving the surveillance performance of wireless receivers indense co-channel signal environments. The tool is agnostic in that it isable to integrate directly with existing surveillance receiverequipment.

2. Description of the Related Art

The advent of advanced third and fourth generation (3G/4G) wirelesscellular and local area network (LAN) radio technology represents a newchallenge to lawful electronic surveillance and reconnaissanceactivities. These new generation radios employ sophisticated waveforms,multichannel processing (MIMO) and powerful error correction coding tomaximize reuse of the frequency spectrum while minimizing radio linkpower between mobile devices and the serving cell transceivers. Theresulting dense co-channel interference (CCI) environment prevents allbut the closest cell sites from being reliably received by conventionalsurveillance receivers. Since the cell coverage from a single tower istypically only a 1 to 2 km range, this significantly impacts theavailable surveillance range. Further, the signals from the distant celltransmitters also interfere with the nearby cell tower signal, reducingits received signal quality as well. This prevents reliable reception ofa cell transmitting from the same tower, and also from the sectorpointed away from the receiver's location. An adversary can be in closeproximity—on the far side of the tower—but remain undetected. Suchlimitations hamper military, law enforcement and other sensitiveoperations.

Lawful electronic surveillance operations currently use directionalantennas to combat co-channel interference and extend the surveillancerange to target cells site transmitters. Two types of directionalantenna technologies are used: log-periodic and parabolic reflector(i.e., dish, grid), each optimized for one or more standard wirelessfrequency bands.

Log periodic (LP) antennas can cover multiple frequency bandssimultaneously, so only a single antenna needs to be installed. However,the LP antenna's main beam is generally too broad to be effective inurban/light-urban terrains which have dozens of cell sites lying withinthe beam.

Parabolic reflector (PR) antennas have had greater success in reducingthe co-channel interference background owing to their narrower beamwidths. To achieve the narrower beam the PR antennas must be relativelylarge (˜1 meter diameter) and cover a single operating frequency.Multiple antennas are required to cover standard cell bands, and eachmust be mechanically steered to each desired cell site in turn. PRantennas will cease to be effective however as the new 4G/LANtechnology—LTE, 802.11n, advanced 3G—replace earlier 2G/3G and Wi-Fiformats. Stand-off surveillance of these signals will require multipleantenna elements, spaced within a few wavelengths of each other. A PRantenna cannot achieve this inter-element spacing without widening itsbeam width, eliminating its CCI mitigation performance.

Accordingly, there remains a need in the art for a system and method foraddressing CCI and improving the range and quality of electronicsurveillance of wireless cell radio signals across varying terrains andcell site densities.

SUMMARY OF THE EMBODIMENTS

The present embodiments are directed to an adaptive phased-arrayprocessing solution, referred to as the Wideband Beamformer System(WBS), which has demonstrated a 10:1 improvement in the range andquality of air link surveillance downlink wireless cell radio signals.The WBS applies wideband frequency-domain adaptive beamforming whichpreprocesses the dense RF signal environment, minimizing the CCI fromeach signal, and then reconstructing a “clean” version of the signal forinput to the existing surveillance receiver(s).

The embodiments combine broadband frequency-domain phased-arrayprocessing with recent technology advances in miniaturized receivers andfully programmable gate arrays (FPGAs) to realize a low SWAP, costeffective solution tailored to forward deployed, fixed and mobile,including airborne, surveillance requirements.

More particularly, a first embodiment is directed to a process forimproving the quality of received radio frequency signals. The processincludes: receiving multiple tuned input signals at a subband adaptivefilter, wherein the multiple tuned input signals are derived frommultiple overlapping wideband radio frequency emitter signals emittedfrom multiple transmitters, decomposing by multiple channelizers themultiple tuned input signals into individual channel signals andproviding individual channel signal data to a weighting algorithmmodule; providing by the weighting algorithm module individualizedweighted filter data for each of the individual channel signals inaccordance with the individual channel signal data to an adaptivebeamformer filter module; supplying by the adaptive beamformer filtermodule the individualized weighted filter data to multiple subbandbeamformer combiners for application to each of the individual channelsignals; reconstructing by the subband adaptive filter the filteredindividual channel signals and providing filtered individual channeloutput signals to a one or more receivers; and receiving the filteredindividual channel output signals at designated channels of the one ormore receivers.

A second embodiment is directed to system for improving the quality ofreception of multiple overlapping radio frequency input signals emittedfrom multiple transmitters. The system includes at least one subbandadaptive filter including multiple channelizers for decomposing themultiple overlapping radio frequency input signals into individualchannel signals, a buffer for extracting individual channel signal data,an adaptive beamformer filter module, multiple subband beamformercombiners, multiple synthesizers; and a weighting algorithm module,wherein the weighting algorithm module receives the individual channelsignal data from the buffer and provides individualized weighted filterdata to the adaptive beamformer filter module responsive thereto; andfurther wherein the adaptive beamformer filter module provides theindividualized weighted filter data to the multiple subband beamformercombiners for application to the individual channel signals.

A third embodiment is directed to process for synthesizing an individualantenna beam pattern to each individual cellular transmitter within apredetermined cellular band to a receiving antenna to optimizesignal-to-noise (SNR) of emitted transmitter signals therefrom. Theprocess includes: scanning a predetermined cellular band andconstructing a database of individual cellular transmitters emittingsignals at or above the predetermined threshold; electronically steeringa high gain antenna beam main lobe at each individual cellulartransmitter emitting a signal at or above a predetermined threshold; andsimultaneously directing antenna nulls in the direction of individualcellular transmitters interfering with each of the other individualcellular transmitters within the predetermined cellular band.

BRIEF SUMMARY OF THE FIGURES

The Summary of the Embodiments, as well as the following DetailedDescription, is best understood when read in conjunction with thefollowing exemplary drawings:

FIG. 1 is a schematic of an exemplary transmitter and receiver scenario,including a wide beamforming system (WBS) in accordance with one or moreembodiments described herein;

FIGS. 2a-2c illustrates exemplary hardware and data flow connectionswhich may be used to implement a WBS in accordance with one or moreembodiments described herein;

FIG. 3 is a schematic of an exemplary WBS implementation and process inaccordance with one or more embodiments described herein;

FIGS. 4a-4c are schematics of varying beamformer weightingimplementations in accordance with signal type;

FIG. 5 is a schematic of dual FPGA beamforming processes of the a WBS inaccordance with one or more embodiments described herein;

FIG. 6 is an exemplary dialog box for configuring mission parameters forWBS processing in accordance with one or more embodiments describedherein;

FIGS. 7a-7d are exemplary dialog boxes for illustrating the scanningprocess outputs from the WBS processing in accordance with one or moreembodiments described herein;

FIGS. 8a-8b are exemplary dialog boxes for illustrating the beamformingprocess inputs and outputs from the WBS processing in accordance withone or more embodiments described herein;

FIG. 9 is an exemplary dialog box for illustrating an input-outputchannel map from the WBS processing in accordance with one or moreembodiments described herein;

FIGS. 10a-10d are exemplary dialog boxes illustrating specific scanningand beamforming results from the WBS processing in accordance with afirst specific exemplary embodiment;

FIGS. 11a-11d are exemplary dialog boxes illustrating specific scanningand beamforming results from the WBS processing in accordance with asecond specific exemplary embodiment;

FIG. 12 illustrates exemplary WBS processing and scanning results froman exemplary test scenario;

FIGS. 13a-13b illustrate exemplary before WBS processing and after WBSprocessing scanning results from an exemplary GSM signal test scenario;

FIGS. 14a-14b illustrate a first channel synchronization output from asingle antenna without WBS beamforming in according with an exemplaryGSM signal test scenario;

FIGS. 15a-15c illustrate a second channel synchronization output from asingle antenna without WBS beamforming in according with an exemplaryGSM signal test scenario; and

FIGS. 16a-16c illustrate a second channel synchronization output from asingle antenna with WBS beamforming in according with an exemplary GSMsignal test scenario.

DETAILED DESCRIPTION

Referring to FIG. 1, a conceptual schematic of a WBS 100 in accordancewith a preferred embodiment is shown. FIG. 1 illustrates arepresentative co-channel environment 15 with multiple individual celltransmitters (hereafter “cell sites”) 20 a-20 e. The varying verticalheight of each cell transmitter is intended to denote its receivedsignal strength at the input to the antenna array 25, with the closesttower 20 e being the strongest. In a conventional (prior art) singleinput surveillance receiver, the strongest signal masks those emanatingfrom the more distant cells (i.e., near-far phenomenon). Withoutadditional processing only the closest cells are recoverable, typicallyno more than 1 km standoff. The input to the antennae array is a denseco-channel RF spectrum wherein all cells are transmitting on the samefrequency channels.

In accordance with the preferred embodiment, the WBS uses phased-arrayprocessing to synthesize a unique antenna beam pattern to eachindividual cell site (tower transmitter) to optimize its signal-to-noise(SNR) ahead of the signal demodulators. This is accomplished byelectronically steering a high gain antenna beam main lobe at the cellcite, while simultaneously directing antenna nulls towards high poweredinterfering cells/towers. Using wideband frequency domain techniques ina wideband adaptive beamformer 30, the signals from multiple cells areisolated, and individually beam formed to attenuate the CCI from itsneighbor cells. The resultant cell site signals 35 a-35 e are thenreconstructed and output to one or more downstream surveillancereceivers 40 for processing. The use of wideband beamforming enables theWBS to isolate all frequency channels for multiple cell sitessimultaneously.

Additionally, the WBS described herein also includes at least thefollowing additional capabilities and advantages. The WBS interfaceswith existing site receivers, i.e., the reconstructed wideband signals35 a-35 e interface directly to legacy wireless surveillance receivers40, using e.g., RF or 10 GigE/Vita 49 formatted digital data. The WBSsupports high capacity output (as needed) with the ability to isolateand output multiple cell channels using frequency stacking; supportingbeamforming and output of up to 48 CDMA2000 channels. The WBSarchitecture supports multiple wireless signal formats and is currentlyprogrammed for, but not limited, 3GPP2 CDMA2000 1×RTT and EVDO cellstandards. Additionally, the WBS architecture supports adaptivebeamforming for all modern cell and LAN radio formatted signals withonly software modifications: i.e., GSM, TD-SCDMA, W-CDMA, LTE, 802.16eWiMAX and 802.11a/g/n Wi-Fi. The WBS employs signal referencedbeamforming as compared to prior art subspace direction of arrival (DOA)solutions. The beamforming solutions are trained on referencesub-channels imbedded in the signal format; the number of signals thatcan be received is not limited by the number of antennas in the array.The WBS supports ad hoc and standard antenna array topologies. That isthe beamforming is array-agnostic, compatible with a wide variety ofstandard or ad hoc antenna array topologies. Further, antenna arrays andRF distribution do not require calibration. Further still, the WBSsupports external direction finding (DF) and geo-location. The WBSbeamforming solutions, receiver calibration and raw data snapshots canassist in DF and geo-location of co-channel transmitters. The datacollects are GPS time stamped to support Time-of-Flight (TOF) andTime-Difference-of-Arrival (TDOA) geo-location methods.

In contrast with prior art solutions, instead of pointing a singlenarrow antenna beam at a desired cell, the WBS synthesizes multiplenulls in the antenna pattern towards strong interfering cells, whileconstraining the main lobe to point at the desired cell. Thephased-array algorithm independently optimizes the antenna pattern foreach desired cell to maximize the signal quality against theinterference background. Multiple cells can be monitored simultaneously.The LP and PR antennas described in the Description of the Related Artmust be physically large to achieve a narrow beam width. Whereas thephased-arrays of the present embodiments can be built using low gainantennas which are smaller and lower cost. Further, a phased array iseasily customized with additional antenna elements, dual polarizedelements, and wider aperture to achieve the CCI and spatial diversityperformance needed to operate against new 4G/LAN signals.

Referring to FIGS. 2a-2c , an exemplary WBS hardware implementation 200is shown. The exemplary implementation includes an 8-channel coherentantenna 225 and a 1U commercial server with an FPGA card 230 (e.g.,Xilinx Kintex7) programmed with the WBS processing functionality(hereafter the “WBS server”). Additional exemplary server details areshown in FIGS. 2b and 2c . In operation, the server 230 accepts 8coherent digitized data streams from a digital tuner 227 (e.g., NDR308from Cyber Radio) over 10 GigE interface formatted links, applies thebeamformer solutions in real-time, and outputs the resultant widebandsignals on 10 GigE outputs to the external receivers 280 (e.g., DigitalReceiver Technology (DRT)). The 10 GigE data use VITA49 link layerformatting. The adaptive algorithms, burst demodulation and controlfunctions are implemented in a single core embedded computer runningLinux 240. System control is implemented through a JAVA GUI applicationwhich runs locally on the embedded computer or remotely across thenetwork. The particular implementation shown in FIGS. 2a was designed tobalance affordability with functionality at both fixed and mobile sites.One skilled in the art recognizes the numerous variations in hardwareand software implementation and additions thereto to support datatransmission and storage. The example provided herein is not intended tobe limiting.

The WBS architecture provides for optimum hardware/softwarepartitioning, wherein the FPGA implements the high-speed, real-timefrequency domain beamformer(s) for each cell. This portion of thedigital signal processing (DSP) is signal invariant, i.e., the same forall wireless signal formats. The WBS architecture is interoperable withexisting site surveillance equipment. The WBS I/O is scalable to 16wideband Rx and 4 wideband outputs; enabling independent multi-bandcoverage, or higher dimensional signal processing to support 2×2 and 4×4MIMO surveillance. Alternatively, the current system can be sub-dividedto support 2 independent, 4-antenna BFs for 80 MHz band coverage.Further, the WBS provides for additional integration with third partyDSP and SDR architectures and supports mixed FPGA and embedded CPUprocessing.

One skilled in the art recognizes that the WBS functionality is notlocked into FGPA hardware, and can support software only solutionsproviding the real-time throughput. For instance, Graphical ProcessingUnits (GPUs) can implement much of the FPGA's core high speed streamingfunctions. Currently COTS GPUs are I/O bound and can support only afraction of the I/O bandwidth of a single FPGA. Thus, at the presenttime, the FPGA-based solution is preferred to meet affordability andlowest SWAP.

The WBS has two primary modes of operation. In the Survey Mode, the WBSscans the cellular band and constructs a database of cell towertransmitters that can be successfully processed by the beamformer.Channel ID and measured beamforming output signal to noise ratios aresent to the GUI for operator review and selection. In the BeamformingMode, the WBS applies the unique beamformer for each selected celltransmitter to the real-time data from the antenna array. The beamformerfor each cell is then periodically recomputed to track changes in the RFand CCI environment.

A more detailed description of the WBS processing is described withreference to FIG. 3 which details the processing steps performed by theWBS processor/server (230, 240). As discussed with reference to FIG. 1,the antenna array receives multiple overlapping wideband signals, i.e.,co-channel input spectrum, from one or more transmitters (cells/towers)located at various distances, elevations and angles from the antennaarray. In FIG. 3, the antenna array 225 is an N-Channel receiver whichoutputs up to 8 RF tuned input signals (hereafter Input Signals) eitherdirectly (or indirectly) to a subband adaptive filtering (SAF) module242. The Input Signals are converted to digital format prior toprocessing at the SAF module 242. At the SAF module 242, the InputSignals are subjected to polyphase FFT (Fast Fourier Transform) atchannelizers 244 to decompose the Input Signals from N antennas intosubbands, i.e., channels, and provided to a delay buffer/data selector246. Selected channel data is provided from the delay buffer/dataselector 246 to a weighting algorithm module 248. The weightingalgorithm module 248 stores signal-of-interest (SOI) specific weightupdate (filter) algorithms which are selectively provided to/updated inan adaptive beamformer (ABF) weight (filter) module 250 responsive tothe selected channel data. In selecting one or more weighting (oradaptive filtering) algorithms, the weight module 250 considers thedetails in the selected channel data including, but not limited to SOIfeatures and direction of arrival; trade-off between good performanceand computation requirements, need for interference and multipathmitigation.

Next, at 252 and 254, the SAF applies the weights (filters) suppliedfrom the adaptive beamformer (ABF) weight (filter) module 250 to thechannels, combines and re-synthesizes resulting scalar channels toreconstruct the co-channel mitigated passband and map different sets ofemitters (transmitters/cells/towers) to different channels and widebandoutput streams. The SAF also includes the ability to translate signalsaround in passband prior to re-synthesizing and output different emittersignals on multiple passbands. The output signals (hereafter OutputSignals) exit the SAF 242 to designated channels at pre-configuredreceivers.

Channelizers (synthesizer) 244 are designed as low pass filters with thefollowing attributes: near perfect reconstruction pseudo-QMF designedusing Iterative Constrained Least Squares; square of the response isNth-band filter; cascade is all pass and >80 dB out-of-band rejectionwhich minimizes channel artifacts belonging to adjacent signals. Anexemplary channelizer (synthesizer) 244 specification includes: 256channels over 51.2 MHz passband; 200 kHz channel spacing; 2048 tap FIR,Q25; Nominal 2× oversampled and Weighted Overlap Add. The channelizer244 can be optimized for specific signal formats (e.g., OFDM).

Referring to FIGS. 4a to 4c , the adaptive signal processing (ASP)architecture described herein is applicable to different signal typeswith minor variations that will be appreciated by those skilled in theart. FIG. 4a is exemplary of the ASP architecture adapted to time-domainerror calculation for OFDM/OFDMA signal types, wherein the processre-synthesizes filtered (scalar) channels to reconstruct SOI anddevelops error signals and re-transform error signals through thecorresponding channelizer to drive filter weight adaption. FIG. 4b isexemplary of the ASP architecture adapted to frequency-domain errorcalculation for GSM signal types, wherein the process transforms areference signal with corresponding K-channel filter bank and computeserror on a per channel basis and adapts filter weights. Finally, FIG. 4cis exemplary of the feed-forward beamformer (FFB) process that isdescribed with reference to FIG. 5 and includes: extraction of each SOIvia digital down-conversion and filtering; developing the S-T beamformersolution for each desired signal channel; stitching together (combining)the solutions from multiple channels to develop the equivalent widebandbeamforming solution and uploading weight solutions to the applicableFPGA.

Referring to FIG. 5, an exemplary FPGA implementation flow for one oftwo duplicative FPGAs included in a WBS in accordance with andembodiment of the present invention is shown. Duplicative andindependent FPGAs are used to process the 8 antenna lanes/streams (4lanes/streams each FPGA). The FPGA coherently digitally down-converts,resamples and channelizes 8 antenna inputs, wherein sampling frequency(Fs)=96 MHz; resampling frequency (Fs′)=51.2 MHz and the Input Signalsare channelized by 256 point FFT with 200 kHz channel spacing. At 40 MHzpassband, the channelizer 244 produces greater than 150 “subband”channels and optimally 200 “subband” channels. Sub-band channels areoversampled based on the amount of input overlap used in thechannelizer. Input overlap will always be approximately 50%.

The delay buffer/memory 246 corner-turns the channel data through theDDRII (or other suitable) memory 248 which involves transposing the 3-Dmatrix from 200×4×M to 4×200×M in each FPGA; wherein M is page/blocksize determined by timing and throughput.

Next, inner product multiplication (dot product) of each subband channelstream by a unique 8×1 weight vector is applied. The weights arecomputed by an embedded (or otherwise accessible) processor anddownloaded to dual-port weight memories 250 and may be updated withouthalting or disrupting the streaming process. Since there are twoindependent FPGAs, partial products are computed on the separate FPGAsand passed across a high speed data link (HSDL) interface (I/F) to formthe full dot product. Two dot products implies two separate andindependent beamformers. Accordingly, the process produces 1×200×Mmatrix on each FPGA.

Next, the channels are mapped and de-channelized, resampled anddigitally up-converted. The de-channelizer 254 uses 256 point FFT withthe same overlap, resampling frequency (Fs′)=51.2 MHz.

In an exemplary use scenario, the primary functions and operations ofthe WBS are configurable by a user through a Java-based user interface(UI). The WBS UI facilitates configuration and control of MissionConfiguration, Survey Mode and Beamforming Mode. A related step in theprocess is Receiver Configuration, which facilitates configuration ofdownstream equipment to receive beamformed signals generated during theBeamforming Mode.

The Mission Configuration process prompts identification of theparameters and values that are required to survey an area for signalcells. A configuration file (band file), e.g., Excel spreadsheet, may beused to list all of the WBS parameter and value requirements including:specifications such as the center of band frequency, the number ofchannels to scan, a list of channels to scan, the frequencies thechannel numbers, etc. An exemplary dialog box 300 for prompting entranceof required parameters and values is shown in FIG. 6. The Band Filebrowse button 305 may be used to select from several preconfigured orcustomizable configuration files for different bands, e.g., CDMA2000,1.2288 MHz. Upon selection of the preconfigured file, default valueswill be populated and may be accepted or customized. In the WBBeamformer section 310, a drop down menu 315 accepts user selection ofthe number of active RF output ports for the mission. The number ofports depends on the number of downstream receiver inputs (1 or 2).Additional features, such as the Auto-detect Carriers setting 320 underthe Tower Survey box provides the ability to configure the mission toscan the band and identify all CDMA carriers, independent of the bandconfiguration file that is being used.

Using Survey Mode, a user is able to identify all of the towers andsectors in the radio field of view. The scope of discovery is determinedby the aperture and elevation of the antenna, and by tower density in anarea. WBS can detect towers up to 26 kilometers, depending on the numberof towers in the area. WBS can estimate tower range for CDMA signaltypes, and can provide precise GPS time stamps for external TDOA-basedgeolocation. FIGS. 7a to 7d illustrate a dialog box snap shot 400 andportions thereof of Survey Mode results in accordance with a MissionConfiguration. Each scanned channel goes through a 2-pass sequence inWBS. WBS cycles through the progress stages twice (Capture/MemTx/Detect) for each channel number: the first time for theomnidirectional antenna to find the towers, and a second time for the 8element antenna to do detection beamforming. Capture is the process ofrecording a snapshot file of the RF environment, Mem Tx is recording asnapshot file for processing and Detect is processing of the snapshotfiles to look for signals.

The dialog box in FIG. 7a includes additional pertinent information foruser review and consideration including: LAN RX which indicates thenumber of messages received by WBS; LAN TX which indicates the number ofmessages sent by WBS during the scan; GPS which may be color coded toindicate status as valid and locked to GPS time, lost signal (e.g., dueto environmental interferences) and bypass mode; Latitude/Longitudewhich is location of the antenna; Heading which is direction antenna ispointing; Signal/Band which is type of signal detected (such as CDMA850)and confirmation that the band of interest has been detected; Channelswhich indicates number of channels scanned; ETI which is elapsed timeindicator since the UI was turned on (this could include multiplemissions/scans/beamforms) and refreshes periodically; and RCVR whichindicates temperature of the antenna in degrees centigrade and may turnsred or emit sound or other signal as a warning when temperature isabove/below ideal, e.g., at 50 degrees centigrade.

The portion 405 of the dialog box 400 shown in FIG. 7b providesinformation under the Survey Results tab 410 and includes identificationof the Cell IDs, signal strengths, and geographic locations of thescanned towers. More particularly, the Survey Results include: ActiveCNs which are channel numbers of the active channels that were scanned(the Active CN of the channel that is currently being scanned turns acolor, e.g., blue, as Survey Mode progresses); Tower icon+Channels whichis how many channels are broadcasting on a tower; CID which is cell IDnumber of a tower; F-PICH SINR (dB) which is Signal to TotalInterference Plus Noise Ratio for the pilot channel; F-SYNCH SINR (dB)which is Signal to Total Interference Plus Noise Ratio for the syncchannel; Range (km) which is uncalibrated range to a tower; LOB (deg)which is line of bearing to a tower from the scan location and Assign toOutput which is used to isolate a tower of interest for beamforming.

The map portion 425 of the dialog box shown in FIG. 7c provides forindividual tower position information overlaid on the map. This view isselected using the Map tab 430 and individual towers are user selectedfrom the Survey Results tab 410 by highlighting a tower in the listing.

Further, the details portion 450 of the dialog box shown in FIG. 7dprovides for a visual representation of relative signal strength andfrequencies from each tower for all detected towers. The number ofdetected and plotted towers under the Details tab 455 may be greaterthan the number of cells (towers) listed under the Survey Results tab410. This is because Survey Results tab 410 only lists results fortowers scoring a pilot or sync subchannel SINR greater than aconfigurable F-SYNC threshold, e.g., 3. The Details results include:CN.CID which is the channel number of the active channel that wasbeamformed and the Cell ID number of its tower; SID:NID which is thesystem ID and network ID of the cell ID; F-PICH SINR (dB) which isSignal to Total Interference Plus Noise Ratio for the pilot channel;F-SYNCH SINR (dB) which is Signal to Total Interference Plus Noise Ratiofor the sync channel; RX Pilot SINR (dB) which is Signal to TotalInterference Plus Noise Ratio for the receive pilot channel; BF PilotSINR (dB) which is Signal to Total Interference Plus Noise Ratio for thecalculated beamformed pilot channel; Range (km) which is uncalibratedrange to a tower; LOB (deg) which is line of bearing to a tower from thescan location; LOB Quality which is estimated quality of the LOBcalculation (a value close to 1 indicates a high quality LOBcalculation); Carrier Freq (Hz) which is receive carrier frequency ofthe examined channel; Pilot Lag (chips) which is measurement of thesignal time offset relative to PN_OFFSET=0 and Pilot RSS (dBm) which ispilot receive signal strength.

In the Beamforming Mode, a user can select one or multiple towers ofinterest for beamforming. The WBS adaptively beamforms each selectedtransmitter from the Survey Mode, mapping the signals across multiple 40MHz outputs. Each signal is output at the original RF and translated tounused portions of the output spectrum for direct input to receivers.FIGS. 8a and 8b illustrate a dialog box snap shot 500 and portionsthereof of Beamforming Mode results in accordance with a MissionConfiguration and selected towers from the Survey Mode results describedabove.

Referring to FIG. 8a , the portion 505 of the dialog box 500 showsselection of multiple individual towers under the survey results listedunder Results tab 510 by selecting the associated boxes in the Assign toOutput column 515. In order to initiate the beamforming process, theuser clicks on the Beamform button 520. Once initiated, the beamformingprocess weights the input from the antennas to null out the mostpowerful signals and to isolate the weaker towers. The dialog box 500continues to provide: LAN RX which indicates the number of messagesreceived by WBS; LAN TX which indicates the number of messages sent byWBS during the scan; GPS which may be color coded to indicate status asvalid and locked to GPS time, lost signal (e.g., due to environmentalinterferences) and bypass mode; Latitude/Longitude which is location ofthe antenna; Heading which is direction antenna is pointing; Signal/Bandwhich is type of signal detected (such as CDMA850) and confirmation thatthe band of interest has been detected; Channels which indicates numberof channels scanned; ETI which is elapsed time indicator since the UIwas turned on (this could include multiple missions/scans/beamforms) andrefreshes periodically; and RCVR which indicates temperature of theantenna in degrees centigrade and may turns red or emit sound or othersignal as a warning when temperature is above/below ideal, e.g., at 50degrees centigrade identification of the Cell IDs, signal strengths, andgeographic locations of the scanned towers.

The portion 525 of the dialog box 500 shown in FIG. 8b provides beamformresults information under the Results tab 510 and includes: CN which arechannel numbers of the active channels that was beamformed; CID which iscell ID number of a tower; OCN which is output channel number; Portwhich is identifies which RF beamformer output the signal is active on(the port number will be either 0 or 1. If only 1 output was previouslyselected, the Port number will always be 0. If 2 output ports wereconfigured, the Port identifies the output port that is being used); LOB(deg) which is line of bearing to a tower from the scan location;Uncalibrated Range (km) which is the uncalibrated range from the antennato a tower; F-PICH Es/Io(dB) which is Signal to Total Interference PlusNoise Ratio for the pilot channel and F-SYNCH Es/Io (dB) which is Signalto Total Interference Plus Noise Ratio for the sync channel. Thebeamform results are constantly updated as the Beamforming Mode is acontinual process. WBS refines the beam weights and adjusts forenvironmental conditions to maintain the weighted channels and to keepstrengthening the tower of interest (for example, if the antenna movesslightly in the wind).

Finally, a user's downstream receivers may be configured to receive thebeamform signals by selecting the View tab (530) on the dialog box 500toolbar as shown in FIGS. 8a and 8b . Under the View tab 530 will be anOutput Map option (not shown) providing access to the Input-OutputChannel Map specifications shown in dialog box 600 of FIG. 9. The dialogbox 600 includes: CID which is cell ID number of a tower; Input CN whichare channel numbers of the active channel that was beamformed; OutputPort which is the output port number identifying the RF beamformeroutput the signal is active on, either 0 or 1; and Output CN which isoutput channel that the signal was remapped to during beamforming. Theuser uses the specifications in 600 to assign output channel numbers(Output CN) to their downstream receivers. WBS stacks the outputs fromthe survey results. As each selected tower is beamformed, WBS translatesthe signals to unused portions of the output spectrum, mapping thesignals to new output channels at the original RF.

FIGS. 10a-10d illustrate a first channel mapping and assignment scenariowherein the Mission Configuration included a single channel, withmultiple towers detected. As shown in FIG. 10a , on channel 384, therewere 14 towers detected. Of these 14 towers, 12 were selected forbeamforming. Referring to FIGS. 10b-10d , WBS maps input channel (InputCN) 384 (FIG. 10c ) to 12 new output channels (Output CN) (FIG. 10d ).In accordance with the Input-Output Channel Map of FIG. 10b , to receivethe beamformed signals from channel 384, the user would assign outputchannels 024, 084, 144, 204, 264, 324, 384, 444, 504, 564, 624, and 684to their downstream receiver.

FIGS. 11a-11d illustrate a second channel mapping and assignmentscenario wherein the Mission Configuration included multiple channels,with multiple towers detected. As shown in FIG. 11a , 17 towers (cells)were detected across 6 channels. Of these 17 towers, 2 (140, 460) wereselected for beamforming, each with 6 channels. Referring to FIGS.11b-11d , WBS maps the 12 input channels (Input CN) (FIGS. 11c ) to 12new output channels (Output CN) (FIG. 11d ). In accordance with theInput-Output Channel Map of FIG. 11b , to receive the beamformed signalsfrom tower (cell) 460 stacked in the 384-589 range, the user wouldassign output channels 024, 065, 106, 147, 188, and 229 to theirdownstream receiver. Similarly, the user would assign output channels384, 425, 466, 507, 548, and 589 to the receiver to capture the datafrom tower 140.

The data volumes produced by the WBS-fed surveillance receivers dependon the density of cell sites, number of sites/channels targeted, cellsignal format and specific parameters of the electronic surveillanceactivity.

A WBS in accordance with the embodiments described herein has beenperformance tested in multiple field trials comprising a wide variety oflocations, terrains, and antenna configurations. In all cases, the WBSprovides for a 10:1 improvement in surveillance range (typically beyond10 km). Referring to FIG. 12, the results from tests comparing thesimultaneous (side-by-side) operation of WBS performance with a highgain directional single LP antenna installation approach are shown. Thesingle high gain antenna recovered only one cell site withsignal-to-noise-ratio (vertical axis in FIG. 12) sufficient for reliablereception. This cell site was measured at 0.9 km distance. Fiveadditional cell sites (#2 through #6) were detected but the receivedcell site signal was below the reception threshold required for reliablereception (approximately 7.0 dB). Using the WBS in line with thesurveillance receiver, the number of recoverable cell sites jumped from1 to 18 as shown in FIG. 12. With the inline WBS, the same 6 cells (#1through #6) had received SNR equal to or greater compared to 1 cell inoriginal configuration. An additional 12 cells. And there was a 10 foldincrease in nominal surveillance range: from 900 meters to 9.9 km.

A modified WBS may also be used to combat CCI and low signal power forsignals transmitted in GSM (and other cellular packet formats, e.g.,GPRS and EDGE). More particularly, a key feature of the WBS architectureand process is that it computes a wideband beamformer solution enablingsimultaneous co-channel interference mitigation of all signalstransmitted by the cell base station transmitters. The beamformer workscorrectly over the entire operating frequency range of the cell network.This is particularly important for GSM surveillance because its usesfrequency hop spread spectrum (FHSS) to mitigate fading and inter-cellinterference. As the name implies, FHSS hops the carrier frequency ofeach signal through a set of pseudo-randomly selected channels which aredistributed across all or part of the GSM operating band. All usertraffic channels and most control channels (e.g., the TCH and SDCCH,respectively) in the GSM network operate in this way.

The only fixed frequency channel in the GSM network is the “beacon”channel which broadcasts synchronization and public network information,and is used by mobiles to sync to and enter the GSM network. The beaconchannel can be used by the modified WBS to handle GSM via a two-stepalgorithm.

First the modified WBS scans for the GSM beacon channel transmitted byeach cell/tower in the radio field of view. The modified WBS thenutilizes the cell beacons to develop a “prototype” antenna pattern foreach detected cell (including co-channel cells). Second, the WBS usesthe prototype pattern to synthesize the equivalent wideband solution.The result is an antenna pattern, unique to each cell transmitter, whichmaintains its performance across the entire GSM operating frequencyband; i.e., the main beam and the antenna nulls continue to be steeredin the correct directions.

In a test of the modified WBS, the modified WBS process 8-antenna arraysnapshots of the GSM Beacons transmitted on 5 different ARFCNs shown inTable 1. No special antenna alignment or array calibration was used orrequired.

TABLE 1 Beacon SNR @ SNR @ SNR Channel Strongest Input BeamformerImprovement ARFCN Antenna (dB) Output (dB) (dB) 128(A) −2.0 10.0 12.0128(B) <0 8.1 8.1 179 5.6 11.5 5.9 181(A) 6.1 7.9 1.8 181(B) −1.9 7.59.4 237 7.4 15.9 8.5 239(A) 22.0 20.7 −1.3 239(B) 16.1 22.0 5.9As illustrated, five (5) separate beacon channels (128, 179, 181, 237and 239) were recorded and processed through the modified WBS. Thespecific GSM network installation used for the test also implemented abeaconing scheme in which two co-channel cells from different cellclusters transmit on the same beacon channel, but the beacon signals aretime-division multiplexed so that only one beacon is active at a time.This was implemented on 3 of the 5 beacon channels (channels 128, 181,239). To distinguish these signals in testing, the beacon signals werearbitrarily assigned to one of two cell clusters, arbitrarily labeled“A” and “B”. As a result there were a total of eight beacon processed on5 RF channels.

Each beam formed beacon was then partially demodulated sufficient tomeasure its “raw” symbol SNR. The same beacon channels received from asingle antenna were demodulated and their SNRs measured for comparisonwith the beamformer results. The demodulator only recovered the “raw”GSM symbols, no channel equalization or subsequent bit level processingwas applied.

Using a single antenna, 3 of the beacon signals on 128A, 128B and 181Bwere unrecoverable, while the beacon SNRs for channels 179 and 181A wereat the GSM receiver threshold (˜6 dB). Using the modified WBS, all eightsignals were recoverable with SNRs well above threshold.

The performance results are listed in Table 1: column 1 is the channelfrequency index (i.e., ARFCN) from the GSM800 band plan and the A/B isused to indicate the cluster; column 2 is the SNR of the demodulatedbeacon signals for the 1 antenna case; column 3 is the SNR of the samebeacon signal after beamforming by the WBS algorithm; and column 4 isthe SNR improvement.

An example of the performance achieved is illustrated in FIGS. 13a and13b . The figure plots the demodulated GSM symbol constellation for thebeacon identified on ARFCN 128, with (FIG. 13b ) and without (FIG. 13a )beamforming. Without the modified WBS, the received signal wasunrecoverable and the synchronization channels were barely detectable.With beamforming the demodulated symbol constellation shows thepre-equalized GSM/GMSK signal structure, and a measured symbolenergy-to-noise ratio above 9 dB.

Further to the GSM example provided herein, FIGS. 14a-14b show output ofthe strongest signal, ARFCN 239 including Common Control Channelsynchronization (CCCH Syncs) (FIG. 14a ) and Synchronization Channelsynchronization (SCH Sync) (FIG. 14b ) without the modified WBSprocessing. Even without the WBS processing, the signals arewell-defined. This is compared to the pre-WBS processing antenna outputsof the weak signal from ARFCN 128 illustrated in FIGS. 15a-15c . Asshown in FIGS. 16a-16c , the most WBS beamforming signal results shownvast improvement, wherein Common Control Channel synchronization (CCCHSyncs) (FIG. 16b ) and Synchronization Channel synchronization (SCHSync) (FIG. 16c ) are well-defined.

In concluding the detailed description, it should be noted that it wouldbe obvious to those skilled in the art that many variations andmodifications can be made to the embodiments without substantiallydeparting from the principles described herein. Also, such variationsand modifications are intended to be included herein within the scope asset forth in the appended claims.

It should be emphasized that the above-described embodiments are merelypossible examples of the implementations, merely set forth for a clearunderstanding of the principles of thereof. Any variations andmodifications may be made to the above-described embodiments of withoutdeparting substantially from the spirit of the principles of theembodiments. All such modifications and variations are intended to beincluded herein within the scope of the disclosure.

The present invention has been described in sufficient detail with acertain degree of particularity. The utilities thereof are appreciatedby those skilled in the art. It is understood to those skilled in theart that the present disclosure of embodiments has been made by way ofexamples only and that numerous changes in the arrangement andcombination of parts may be resorted without departing from the spiritand scope thereof.

We claim:
 1. A process for improving the quality of received radiofrequency signals comprising: receiving multiple tuned input signals ata subband adaptive filter, wherein the multiple tuned input signals arederived from multiple overlapping wideband radio frequency emittersignals emitted from multiple transmitters, decomposing by multiplechannelizers the multiple tuned input signals into individual channelsignals and providing individual channel signal data to a weightingalgorithm module; providing by the weighting algorithm moduleindividualized weighted filter data for each of the individual channelsignals in accordance with the individual channel signal data to anadaptive beamformer filter module; supplying by the adaptive beamformerfilter module the individualized weighted filter data to multiplesubband beamformer combiners for application to each of the individualchannel signals; reconstructing by the subband adaptive filter thefiltered individual channel signals and providing filtered individualchannel output signals to a one or more receivers; and receiving thefiltered individual channel output signals at designated channels of theone or more receivers.
 2. The process according to claim 1, wherein theindividual channel signal data includes signal-of-interest (SOI)features and direction of arrival data.
 3. The process according toclaim 1, wherein reconstructing by the subband adaptive filtering modulethe filtered individual channel signals includes: applying by themultiple subband beamformer combiners the received individualizedweighted filter data; combining by the multiple subband beamformercombiners subbands within each of the filtered individual channelsignals; and re-synthesizing by multiple synthesizers individual scalarchannel signals from the multiple subband beamformer combiners.
 4. Theprocess according to claim 3, further comprising: translating around inpassband by the subband adaptive filter the individual scalar channelsignals prior to re-synthesizing and outputting different emittersignals on multiple passbands.
 5. The process according to claim 3,further comprising: intercepting at an antenna array multipleoverlapping wideband radio frequency emitter signals emitted frommultiple transmitters; and outputting by the antenna array multipletuned input signals.